What causes loose bodies in the knee?

Injury

A kneecap dislocation is a classic cause in teenagers and young adults: as the kneecap slips out and snaps back, it can shear off a piece of cartilage and bone from its underside or from the thigh bone. Twisting injuries in football, padel or basketball and direct blows can also chip the joint surface. These fragments often appear soon after the injury, sometimes with a large, bloody swelling.

Osteochondritis dissecans (OCD)

In OCD, a small area of bone just beneath the cartilage loses its blood supply and weakens, most often on the inner femoral condyle in children and young adults. If it is not healing, the fragment can loosen and eventually separate, leaving a defect in the joint surface and a loose body in the knee. This is one reason OCD is monitored closely.

Arthritis and less common causes

• Osteoarthritis: bony spurs and flakes of worn cartilage can break off, often in older adults
• Synovial chondromatosis: a rare condition where the joint lining forms many small cartilage nodules
• A previous fracture in or near the joint
• Fragments left after earlier surgery or injury that were not removed

Why the cause matters

Removing a loose body treats the catching and locking, but the place it came from may also need attention. A large fresh fragment in a young patient can sometimes be fixed back in place. A kneecap that dislocates may need stabilising. Arthritis needs its own plan.

At Aman Hospital in Doha, Dr. Gelber uses X-rays and MRI to identify both the fragment and its source before recommending treatment.